a) Field of the Invention
The present invention relates to a musical tone signal processing apparatus capable of generating an internal sync clock when an external sync clock becomes abnormal.
b) Description of the Related Art
Recent developments on networks allow a plurality of electronic musical instruments connected to networks to be played synchronously. As the standard specifications for communications between electronic musical instruments, Musical Instrument Digital Interface (MIDI) is known. Tempo clocks (F8) are used as timing signals for a synchronous performance between some of a plurality of electronic musical instruments or musical tone signal processing apparatuses connected to a network using MIDI. The tempo signal is converted into a MIDI signal and transmitted to other instruments or apparatuses via MIDI cables. Synchronously with this tempo clocks, the other instruments or apparatuses play a music performance.
Recent electronic musical instruments or musical tone signal processing apparatuses use high speed network connections such as USB and IEEE 1394 to realize faster synchronous performance. Synchronous performance is now possible not only at the level of simple automatic performance of MIDI signals but also at the level of reproduction timings of musical tone signal waveforms.
For synchronous performance at the level of timings of waveforms, a sync signal is generated from at least one of a plurality of electronic musical instruments or musical tone signal processing apparatuses connected to a high speed network using USB, IEEE 1394 or the like. This sync signal is very fast as compared to a MIDI signal. Therefore, this sync signal can be used not only for simple synchronous performance but also for timing clocks of a sound generator which reads waveforms.
Each of electronic musical instruments or musical tone signal processing apparatuses receives fast timing clocks from a high speed network, and performs a read operation, a reproduction operation or the like of waveform data synchronously with the received clocks.
More specifically, reproduction sampling clocks are generated in accordance with received sync data (such as a time stamp) and supplied to a sound generator (made of LSI or the like) as its clocks. In this manner, synchronous performance between instruments or apparatuses becomes possible at the level of read timings of waveform data.
Network troubles such as disconnection and transfer abnormality may occur during synchronous performance on the network interconnecting a plurality of electronic musical instruments or musical tone signal processing apparatuses. In such a case, data integrity or data transfer is not possible among some instruments or apparatuses. For example, if F8 does not reach unexpectedly during synchronous performance of MIDI data, each instrument or apparatus performs a dump process of the tone generator to effect an instant muting process.
It is therefore possible to prevent continuous reproduction of sounds or generation of abnormal noises to be caused upon occurrence of discontinuous phenomena.
In such a system in which sampling clocks are generated in accordance with sync data received from a high speed network and used as synchronizing clocks of a tone generator, however, if sampling clocks are suspended or become abnormal from some reasons, the tone generator itself cannot operate normally because of an abnormal state of its sampling clocks.
For example, even if the tone generator is instructed to execute the dump process, the muting process cannot be effected. Therefore, sounds continue to be reproduced or abnormal noises are generated.